Bacteria From Marine Sponges: A Source of New Drugs

Bactericidal effect of bacteria isolated from the marine sponges Hymeniacidon perlevis and Halichondria panicea against carbapenem-resistant Acinetobacter baumannii

In this study, we evaluated the antimicrobial activity of bacteria isolated from the marine sponges Hymeniacidon perlevis and Halichondria panicea against seven Acinetobacter baumannii strains, the majority of which were clinically relevant carbapenem-resistant A. baumannii strains. We observed the inhibitory activity of 18 (out of 114) sponge-isolated bacterial strains against all A. baumanii strains using medium-throughput solid agar overlay assays. These inhibitory strains belonged to the genera Lactococcus, Pseudomonas, and Vagococcus. In addition, this antimicrobial activity was validated through a liquid co-cultivation challenge using an inhibitory strain of each genus and a green fluorescent protein-tagged A. baumanii strain. Fluorescence measurements indicated that the growth of A. baumanii was inhibited by the sponge isolates. In addition, the inability of A. baumanii to grow after spreading the co-cultures on solid medium allowed us to characterize the activity of the sponge isolates as bactericidal. In conclusion, this study demonstrates that marine sponges are a reservoir of bacteria that deserves to be tapped for antibiotic discovery against A. baumanii.

Comprehensive updates on the biological features and metabolic potential of the versatile extremophilic actinomycete Nocardiopsis dassonvillei

Nocardiopsis dassonvillei prevails under harsh environmental conditions and the purpose of this review is to highlight its biological features and recent biotechnological applications. The organism prevails in salt-rich soils/marine systems and some strains endure extreme temperatures and pH. A few isolates are associated with marine organisms and others cause human diseases. Comparative genomic analysis indicates its versatility in producing biotechnologically relevant metabolites. Antimicrobial, cytotoxic, anticancer and growth promoting biomolecules are obtained from this organism. It also synthesizes biotechnologically important enzymes. Bioactive compounds and enzymes obtained from this actinomycete provide evidence regarding its metabolic competence and its potential economic value.

Topical delivery of seriniquinone for treatment of skin cancer and fungal infections is enabled by a liquid crystalline lamellar phase

Seriniquinone (SQ) was initially described by our group as an antimelanoma drug candidate and now also as an antifungal drug candidate. Despite its promising in vitro effects, SQ translation has been hindered by poor water-solubility. In this paper, we described the challenging nanoformulation process of SQ, which culminated in the selection of a phosphatidylcholine-based lamellar phase (PLP1). Liposomes and nanostructured lipid carriers were also evaluated but failed to encapsulate the compound. SQ-loaded PLP1 (PLP1-SQ) was characterized for the presence of sedimented or non-dissolved SQ, rheological and thermal behavior, and irritation potential with hen's egg test on the chorioallantoic membrane (HET-CAM). PLP1 influence on transepidermal water loss (TEWL) and skin penetration of SQ was assessed in a porcine ear skin model, while biological activity was evaluated against melanoma cell lines (SK-MEL-28 and SK-MEL-147) and C. albicans SC5314. Despite the presence of few particles of non-dissolved SQ (observed under the microscope 2 days after formulation obtainment), PLP1 tripled SQ retention in viable skin layers compared to SQ solution at 12 h. This effect did not seem to relate to formulation-induced changes on the barrier function, as no increases in TEWL were observed. No sign of vascular toxicity in the HET-CAM model was observed after cutaneous treatment with PLP1. SQ activity was maintained on melanoma cells after 48 h-treatment (IC50 values of 0.59-0.98 µM) whereas the minimum inhibitory concentration (MIC) against C. albicans after 24 h-treatment was 32-fold higher. These results suggest that a safe formulation for SQ topical administration was developed, enabling further in vivo studies.

Profiling Prokaryotic Communities and Aaptamines of Sponge Aaptos suberitoides from Tulamben, Bali

Sponges (Porifera) harbor a diversity of microorganisms that contribute largely to the production a vast array of bioactive compounds. The microorganisms associated with sponge have an important impact on the chemical diversity of the natural products. Herein, our study focuses on an Aaptos suberitoides commonly found in Indonesia. The objective of this study was to investigate the profile of prokaryotic community and the presence of aaptamine metabolites in sponge Aaptos suberitoides. Sponges were collected from two site locations (Liberty Wreck and Drop Off) in Tulamben, Bali. The sponges were identified by barcoding DNA cytochrome oxidase subunit I (COI) gene. The profile of prokaryotic composition was investigated by amplifying the 16S rRNA gene using primers 515f and 806r to target the V4 region. The metabolites were analyzed using LC-MS, and dereplication was done to identify the aaptamines and its derivates. The barcoding DNA of the sponges confirmed the identity of samples as Aaptos suberitoides. The prokaryotic communities of samples A. suberitoides were enriched and dominated by taxa Proteobacteria, Chloroflexi, Actinobacteria, and Acidobacteria. The chemical analysis showed that all sponges produce aaptamine and isoaaptamine except A. suberitoides S2421 produce analog of aaptamines. This is the first report on the profile of prokaryotic community and the aaptamine of tropical marine sponges, A. suberitoides, from Tulamben, Bali.

Advances in Natural Products from the Marine-Sponge-Associated Microorganisms with Antimicrobial Activity in the Last Decade

Microorganisms are the dominating source of food and nutrition for sponges and play an important role in sponge structure, chemical defense, excretion and evolution. In recent years, plentiful secondary metabolites with novel structures and specific activities have been identified from sponge-associated microorganisms. Additionally, as the phenomenon of the drug resistance of pathogenic bacteria is becoming more and more common, it is urgent to discover new antimicrobial agents. In this paper, we reviewed 270 secondary metabolites with potential antimicrobial activity against a variety of pathogenic strains reported in the literature from 2012 to 2022. Among them, 68.5% were derived from fungi, 23.3% originated from actinomycetes, 3.7% were obtained from other bacteria and 4.4% were discovered using the co-culture method. The structures of these compounds include terpenoids (13%), polyketides (51.9%), alkaloids (17.4%), peptides (11.5%), glucosides (3.3%), etc. Significantly, there are 124 new compounds and 146 known compounds, 55 of which have antifungal activity in addition to antipathogenic bacteria. This review will provide a theoretical basis for the further development of antimicrobial drugs.

Antimicrobial Biosynthetic Potential and Phylogenetic Analysis of Culturable Bacteria Associated with the Sponge Ophlitaspongia sp. from the Yellow Sea, China

Sponge-derived bacteria are considered to be a promising source of novel drugs, owing to their abundant secondary metabolites that have diverse biological activities. In this study, we explored the antimicrobial biosynthetic potential and phylogenetics of culturable bacteria associated with the sponge Ophlitaspongia sp. from the Yellow Sea, China. Using culture-dependent methods, we obtained 151 bacterial strains, which were then analysed for their antimicrobial activities against seven indicator strains. The results indicate that 94 (62.3%) of the 151 isolated strains exhibited antimicrobial activities and inhibited at least one of the indicator strains. Fifty-two strains were selected for further phylogenetic analysis using 16S rRNA gene sequencing, as well as for the presence of polyketide synthase (PKS) and non-ribosomal peptide synthetase (NRPS) genes. These 52 strains belonged to 20 genera from 18 families in 4 phyla, including Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria. Five strains with PKS genes and ten strains with NRPS genes were detected. Among them, two strains contained both PKS and NRPS genes. Notoacmeibacter sp. strain HMA008 (class Alphaproteobacteria) exhibited potent antimicrobial activity; thus, whole genome sequencing methods were used to analyse its secondary metabolite biosynthetic gene clusters. The genome of HMA008 contained 12 biosynthetic gene clusters that potentially encode secondary metabolites belonging to compound classes such as non-ribosomal peptides, prodigiosin, terpene, β-lactones, and siderophore, among others. This study indicates that the sponge Ophlitaspongia sp. harbours diverse bacterial strains with antimicrobial properties and may serve as a potential source of bioactive compounds.

Exploring the Antibiotic Production Potential of Heterotrophic Bacterial Communities Isolated from the Marine Sponges Crateromorpha meyeri, Pseudaxinella reticulata, Farrea similaris, and Caulophacus arcticus through Synergistic Metabolomic and Genomic Analyses

The discovery of novel secondary metabolites is actively being pursued in new ecosystems. Sponge-associated bacteria have been in the limelight in recent years on account of their ability to produce bioactive compounds. In this study, heterotrophic bacteria associated with four sponge species were isolated, taxonomically identified, and subjected to screening for the production of bioactive entities against a panel of nine microorganisms, including Gram-positive and negative bacteria, as well as yeast and fungi. Of the 105 isolated strains, 66% were represented by Proteobacteria, 16% by Bacteriodetes, 7% by Actinobacteria, and 11% by Firmicutes. Bioactivity screening revealed that 40% of the total isolated strains showed antimicrobial activity against one or more of the target microorganisms tested. Further, active extracts from selective species were narrowed down by bioassay-guided fractionation and subsequently identified by HR-ESI-MS analyses to locate the active peaks. Presumably responsible compounds for the observed bioactivities were identified as pentadecenoic acid, oleic acid, and palmitoleic acid. One isolate, Qipengyuania pacifica NZ-96T, based on 16S rRNA novelty, was subjected to comparative metabolic reconstruction analysis with its closest phylogenetic neighbors, revealing 79 unique functional roles in the novel isolate. In addition, genome mining of Qipengyuania pacifica NZ-96T revealed three biosynthetic gene clusters responsible for the biosynthesis of terpene, beta lactone, lasso peptide, and hserlactone secondary metabolites. Our results demonstrate the ability to target the sponge microbiome as a potential source of novel microbial life with biotechnological potential.

Investigation of Global Trends of Pollutants in Marine Ecosystems around Barrang Caddi Island, Spermonde Archipelago Cluster: An Ecological Approach

High-quality marine ecosystems are free from global trending pollutants’ (GTP) contaminants. Accuracy and caution are needed during the exploitation of marine resources during marine tourism to prevent future ecological hazards that cause chain effects on aquatic ecosystems and humans. This article identifies exposure to GTP: microplastic (MP); polycyclic aromatic hydrocarbons (PAH); pesticide residue (PR); heavy metal (HM); and medical waste (MW), in marine ecosystems in the marine tourism area (MTA) area and Barrang Caddi Island (BCI) waters. A combination of qualitative and quantitative analysis methods were used with analytical instruments and mathematical formulas. The search results show the average total abundance of MPs in seawater (5.47 units/m³) and fish samples (7.03 units/m³), as well as in the sediment and sponge samples (8.18 units/m³) and (8.32 units/m³). Based on an analysis of the polymer structure, it was identified that the dominant light group was MPs: polyethylene (PE); polypropylene (PP); polystyrene (PS); followed by polyamide-nylon (PA); and polycarbonate (PC). Several PAH pollutants were identified in the samples. In particular, naphthalene (NL) types were the most common pollutants in all of the samples, followed by pyrene (PN), and azulene (AZ). Pb⁺² and Cu⁺² pollutants around BCI were successfully calculated, showing average concentrations in seawater of 0.164 ± 0.0002 mg/L and 0.293 ± 0.0007 mg/L, respectively, while in fish, the concentrations were 1.811 ± 0.0002 µg/g and 4.372 ± 0.0003 µg/g, respectively. Based on these findings, the BCI area is not recommended as a marine tourism destination.

Marine microbial bioprospecting: Exploitation of marine biodiversity towards biotechnological applications-a review

The increase in the human population causes an increase in the demand for nutritional supplies and energy resources. Thus, the novel, natural, and renewable resources became of great interest. Here comes the optimistic role of bioprospecting as a promising tool to isolate novel and interesting molecules and microorganisms from the marine environment as alternatives to the existing resources. Bioprospecting of marine metabolites and microorganisms with high biotechnological potentials has gained wide interest due to the variability and richness of the marine environment. Indeed, the existence of extreme conditions that increases the adaptability of marine organisms, especially planktons, allow the presence of interesting biological species that are able to produce novel compounds with multiple health benefits and high economical value. This review aims to provide a comprehensive overview of marine microbial bioprospecting as a growing field of interest. It emphasizes functional bioprospecting that facilitates the discovery of interesting metabolites. Marine bioprospecting was also discussed from a legal aspect for the first time, focusing on the shortcomings of international law. We also summarized the challenges facing bioprospecting in the marine environment including economic feasibility issues.

Antarctic Porifera homogenates as a source of enzymes and antibacterial substances: first results

Marine Porifera (sponges) are known to produce several bioactive metabolites having a biotechnological potential, mostly derived from their bacterial symbionts; however, current knowledge on the production of metabolites such as enzymes and antibacterial molecules in sponges living in Antarctic environments is not fully exhaustive and needs further deepened investigation. The interest in discovering the broad spectrum of natural products potentially derived from species adapted to colonize extreme environments stimulates the research toward Antarctic sponge bioprospection. In this study, whole homogenates of Antarctic Demospongiae, belonging to five different species [Haliclona (Rhizoniera) sp., Haliclona (Rhizoniera) dancoi, Microxina sarai, Dendrilla antarctica, and Mycale acerata] were collected from Terra Nova Bay (Ross Sea) and examined for presence and activity of enzymes, including lysozyme, and antibacterial substances. Enzyme activities (leucine aminopeptidase, beta-glucosidase, and alkaline phosphatase) were measured using fluorogenic substrates; lysozyme content was determined on plates containing lyophilized Micrococcus lysodeikticus cell walls as a substrate. Homogenates were screened in microtiter plates for their antibacterial activity against Antarctic bacterial isolates, and the absorbance reduction was measured with a microplate reader. All homogenates exhibited proteolytic, glycolytic, and phosphatasic activities, lysozyme and antibacterial activities at near “in situ” temperature (5 °C), with some differences among the examined species. Results confirmed that Antarctic sponge homogenates are interesting sources of different bioactive substances, likely produced from associated bacterial symbionts, and that could have great potential to be used in medicine or industrial applications.

Discovery and Characterization of Marinsedin, a New Class II Lanthipeptide Derived from Marine Bacterium Marinicella sediminis F2T

Microbial natural products provide a large number of drug leads. It is believed that abundant unexploited marine microorganisms also exhibit great potential for discovering compounds with novel chemical scaffolds and bioactivities. Lanthipeptides are a group of ribosomally synthesized and post-translationally modified peptides exhibiting a variety of biological functionalities. They are characterized by the presence of the thioether-containing bis-amino acids lanthionine and methyllanthionine. However, marine-derived lanthipeptides remain underexplored. Here we identified, heterologously expressed, and structurally characterized the unprecedented class II lanthipeptide marinsedin from the rare marine bacterium Marinicella sediminis F2^T. Marinsedin consists of 19 amino acids and contains a rare 2-oxobutyryl group blocking the N-terminus of the peptide chain and two overlapping intramolecular thioether rings including an unusual 12-membered macro-thioether ring. Furthermore, we also evaluated the biological activity of marinsedin, demonstrating that it exhibits moderate cytotoxicity against HeLa cells and weak cytotoxicity against HCT-116 cell lines.

Fermentation optimization and amylase activity of endophytic Bacillus velezensis D1 isolated from corn seeds

AIMS

In order to acquire quality amylase adopted in practical applications, endophytic bacteria were identified as Bacillus velezensis strain D1 by isolating it from corn seeds. The fermentation conditions and amylase properties of the strain were investigated.

METHODS AND RESULTS

The strain D1 was identified via morphological, physiological, and 16S rDNA phylogenetic analysis. The fermentation conditions of secreted amylase were optimized by single factor and orthogonal experiments. The α-amylase gene was expressed in E. coli and purified by means of immobilized metal ion affinity chromatography (IMAC), upon which the enzyme activity of purified recombinant α-amylase was determined. The results outlined that (1) the strain D1 was identified as Bacillus velezensis. (2) The optimized fermentation conditions for maximum amylase yields included 44 °C for 48 h at pH 7.5. (3) The enzyme had an optimal reaction temperature of 60 °C with strong activity at 50°C and tolerance to 4-hour incubation at 70°C. (4) The enzyme was strongly acid resistant and tolerated at pH5.0-6.0 while the optimal pH was 8.0. (5) Besides, the amylase activity was elevated by the presence of Ca²⁺ and Cu²⁺ . (6) The activity of purified recombinant amylase was 20.59 U/mL under optimal conditions, nearly 7 times that of crude amylase preparations.

CONCLUSIONS

The amylase produced by this strain is strongly tolerant towards acid and high temperatures.

SIGNIFICANCE AND IMPACT OF THE STUDY

Amylases with thermophilic and acid-resistant characteristics are useful for a wide range of applications in food, brewing, textile, starch, paper, and deterrent industries. The enzyme from Bacillus velezensis D1 can be effectively used in different industries.

Bacteria Cultivated From Sponges and Bacteria Not Yet Cultivated From Sponges-A Review

The application of high-throughput microbial community profiling as well as "omics" approaches unveiled high diversity and host-specificity of bacteria associated with marine sponges, which are renowned for their wide range of bioactive natural products. However, exploration and exploitation of bioactive compounds from sponge-associated bacteria have been limited because the majority of the bacteria remains recalcitrant to cultivation. In this review, we (i) discuss recent/novel cultivation techniques that have been used to isolate sponge-associated bacteria, (ii) provide an overview of bacteria isolated from sponges until 2017 and the associated culture conditions and identify the bacteria not yet cultured from sponges, and (iii) outline promising cultivation strategies for cultivating the uncultivated majority of bacteria from sponges in the future. Despite intensive cultivation attempts, the diversity of bacteria obtained through cultivation remains much lower than that seen through cultivation-independent methods, which is particularly noticeable for those taxa that were previously marked as "sponge-specific" and "sponge-enriched." This poses an urgent need for more efficient cultivation methods. Refining cultivation media and conditions based on information obtained from metagenomic datasets and cultivation under simulated natural conditions are the most promising strategies to isolate the most wanted sponge-associated bacteria.

Sponges and Their Symbionts as a Source of Valuable Compounds in Cosmeceutical Field

In the last decades, the marine environment was discovered as a huge reservoir of novel bioactive compounds, useful for medicinal treatments improving human health and well-being. Among several marine organisms exhibiting biotechnological potential, sponges were highlighted as one of the most interesting phyla according to a wide literature describing new molecules every year. Not surprisingly, the first marine drugs approved for medical purposes were isolated from a marine sponge and are now used as anti-cancer and anti-viral agents. In most cases, experimental evidence reported that very often associated and/or symbiotic communities produced these bioactive compounds for a mutual benefit. Nowadays, beauty treatments are formulated taking advantage of the beneficial properties exerted by marine novel compounds. In fact, several biological activities suitable for cosmetic treatments were recorded, such as anti-oxidant, anti-aging, skin whitening, and emulsifying activities, among others. Here, we collected and discussed several scientific contributions reporting the cosmeceutical potential of marine sponge symbionts, which were exclusively represented by fungi and bacteria. Bioactive compounds specifically indicated as products of the sponge metabolism were also included. However, the origin of sponge metabolites is dubious, and the role of the associated biota cannot be excluded, considering that the isolation of symbionts represents a hard challenge due to their uncultivable features.

Immunomodulatory properties of characellide A on human peripheral blood mononuclear cells

Marine sponges and their associated microbiota are multicellular animals known to produce metabolites with interesting pharmacological properties playing a pivotal role against a plethora of pathologic disorders such as inflammation, cancer and infections. Characellide A and B belong to a novel class of glycolipopeptides isolated from the deep sea marine sponge Characella pachastrelloides. In this study, we have evaluated the effects of characellide A and B on cytokine and chemokine release from human peripheral blood mononuclear cells (PBMC). Characellide A induces a concentration- and time-dependent CXCL8, IL-6 and TNF-α release from PBMC. This production is mediated by the induction of gene transcription. Moreover, cytokine/chemokine release induced by characellide A from PBMC is CD1d-dependent because a CD1d antagonist, 1,2-bis(diphenylphosphino)ethane [DPPE]-polyethylene glycolmonomethylether [PEG], specifically inhibits characellide A-induced activation of PBMC. In conclusion, characellide A is a novel modulator of adaptative/innate immune responses. Further studies are needed to understand its potential pharmacological application.

Antibiotics from Marine Bacteria

This review discusses main directions and results of the studies on antibiotics produced by bacteria living in the marine environment. In recent years many obligate marine species and strains were studied, diverse metabolites were isolated, and their chemical structures were elucidated. Among them here were natural compounds toxic against tumor cells, pathogenic bacteria, viruses, and malaria plasmodial species; these compounds often had no analogues among the natural products of terrestrial origin. Some isolated compounds form a basis of active ingredients in medicinal preparations used in clinic practice, while others are under different stages of preclinical or clinical studies. Much attention has been paid in recent years to producers of marine-derived antibiotics isolated from the deep-sea habitats, from the surface of marine invertebrates and algae, as well as from symbiotic microorganisms.

Anti-tumour drugs of marine origin currently at various stages of clinical trials (review)

Oncological diseases for a long time have remained one of the most significant health problems of modern society, which causes great losses in its labour and vital potential. Contemporary oncology still faces unsolved issues as insufficient efficacy of treatment of progressing and metastatic cancer, chemoresistance, and side-effects of the traditional therapy which lead to disabilities among or death of a high number of patients. Development of new anti-tumour preparations with a broad range of pharmaceutical properties and low toxicity is becoming increasingly relevant every year. The objective of the study was to provide a review of the recent data about anti-tumour preparations of marine origin currently being at various phases of clinical trials in order to present the biological value of marine organisms – producers of cytotoxic compounds, and the perspectives of their use in modern biomedical technologies. Unlike the synthetic oncological preparations, natural compounds are safer, have broader range of cytotoxic activity, can inhibit the processes of tumour development and metastasis, and at the same time have effects on several etiopathogenic links of carcinogenesis. Currently, practical oncology uses 12 anti-tumour preparations of marine origin (Fludarabine, Cytarabine, Midostaurin, Nelarabine, Eribulin mesylate, Brentuximab vedotin, Trabectedin, Plitidepsin, Enfortumab vedotin, Polatuzumab vedotin, Belantamab mafodotin, Lurbinectedin), 27 substances are at different stages of clinical trials. Contemporary approaches to the treatment of oncological diseases are based on targeted methods such as immune and genetic therapies, antibody-drug conjugates, nanoparticles of biopolymers, and metals. All those methods employ bioactive compounds of marine origin. Numerous literature data from recent years indicate heightened attention to the marine pharmacology and the high potential of marine organisms for the biomedicinal and pharmaceutic industries.

The Distribution and Antibacterial Activity of Marine Sponge-Associated Bacteria in the Aegean Sea and the Sea of Marmara, Turkey

The distribution and antibacterial activities of bacteria isolated from fifty-five marine sponge samples collected from the Aegean Sea and the Sea of Marmara were investigated in the period between 2011 and 2013. The antibacterial activities of the methanolic extracts of marine sponge-associated bacteria tested against six pathogenic bacteria: Staphylococcus aureus SA1 and SA2, Brucella melitensis B37, Vibrio vulnificus GK23, Escherichia coli O157:H7 (ATCC 35150), and Salmonella enterica subsp. enterica serovar typhi (ATCC 167), using disk diffusion tests and minimum inhibitory concentration technique. The bacteria isolated from sponges and ambient seawater samples were identified using VITEK 2 Compact 30 automated microbial identification system. All bacterial extracts were exhibited antibacterial activity with various MIC values ranging from 7.8 mg/ mL to 1000 mg/mL against all pathogenic bacteria tested. The antibacterial efficacy rates found to be higher in the Aegean Sea than the Sea of Marmara samples. Fifty-five sponge samples belonging to fifteen species and host twenty-two bacterial species belonging to seven classes in two different marine areas at varying rates were detected. The most common sponge-associated bacterium was recorded as Sphingomonas paucimobilis and Bacillus cereus in the Aegean Sea and the Sea of Marmara, respectively. The composition and counts of the sponge-associated bacteria were found significantly higher than the free-living bacteria in the ambient sea water sampling points of both two marine areas. The presence of high antibacterial potential of sponge-related bacteria obtained in this study provided data for further studies on marine-derived antimicrobial agents, including the effects of environmental differences.

Antimicrobial Activities of Marine Sponge-Associated Bacteria

The misuse and overuse of antibiotics have led to the emergence of multidrug-resistant microorganisms, which decreases the chance of treating those infected with existing antibiotics. This resistance calls for the search of new antimicrobials from prolific producers of novel natural products including marine sponges. Many of the novel active compounds reported from sponges have originated from their microbial symbionts. Therefore, this study aims to screen for bioactive metabolites from bacteria isolated from sponges. Twelve sponge samples were collected from South Australian marine environments and grown on seven isolation media under four incubation conditions; a total of 1234 bacterial isolates were obtained. Of these, 169 bacteria were tested in media optimized for production of antimicrobial metabolites and screened against eleven human pathogens. Seventy bacteria were found to be active against at least one test bacterial or fungal pathogen, while 37% of the tested bacteria showed activity against Staphylococcus aureus including methicillin-resistant strains and antifungal activity was produced by 21% the isolates. A potential novel active compound was purified possessing inhibitory activity against S. aureus. Using 16S rRNA, the strain was identified as Streptomyces sp. Our study highlights that the marine sponges of South Australia are a rich source of abundant and diverse bacteria producing metabolites with antimicrobial activities against human pathogenic bacteria and fungi.

Selection of sponge-associated bacteria with high potential for the production of antibacterial compounds

The potential of sponge-associated bacteria for the biosynthesis of natural products with antibacterial activity was evaluated. In a preliminary screening 108 of 835 axenic isolates showed antibacterial activity. Active isolates were identified by 16S rRNA gene sequencing and selection of the most promising strains was done in a championship like approach, which can be done in every lab and field station without expensive equipment. In a competition assay, strains that inhibited most of the other strains were selected. In a second round, the strongest competitors from each host sponge competed against each other. To rule out that the best competitors selected in that way represent similar strains with the same metabolic profile, BOX PCR experiments were performed, and extracts of these strains were analysed using metabolic fingerprinting. This proved that the strains are different and have various metabolic profiles, even though belonging to the same genus, i.e. Bacillus. Furthermore, it was shown that co-culture experiments triggered the production of compounds with antibiotic activity, i.e. surfactins and macrolactin A. Since many members of the genus Bacillus possess the genetic equipment for the biosynthesis of these compounds, a potential synergism was analysed, showing synergistic effects between C14-surfactin and macrolactin A against methicillin-resistant Staphylococcus aureus (MRSA).

Role of symbiosis in the discovery of novel antibiotics

Antibiotic resistance has been an ongoing challenge that has emerged almost immediately after the initial discovery of antibiotics and requires the development of innovative new antibiotics and antibiotic combinations that can effectively mitigate the development of resistance. More than 35,000 people die each year from antibiotic resistant infections in just the United States. This signifies the importance of identifying other alternatives to antibiotics for which resistance has developed. Virtually, all currently used antibiotics can trace their genesis to soil derived bacteria and fungi. The bacteria and fungi involved in symbiosis is an area that still remains widely unexplored for the discovery and development of new antibiotics. This brief review focuses on the challenges and opportunities in the application of symbiotic microbes and also provides an interesting platform that links natural product chemistry with evolutionary biology and ecology.

Diversity and antimicrobial potential of Actinobacteria isolated from diverse marine sponges along the Beibu Gulf of the South China Sea

Marine sponge-associated microorganisms have proven to be a very promising source of biologically active and pharmaceutically important natural products. In this study, we investigated the diversity and antibacterial potential of bacteria from 49 sponge species isolated from the Beibu Gulf, South China Sea, belonging to 16 genera and several unidentified taxa. Using a variety of selective media, 363 strains with different morphologies were identified to six bacterial taxa, including Proteobacteria (α-subgroup 85 and γ-subgroup 59), Actinobacteria (123), Firmicutes (90), Bacteroidetes (5) and Brevundimonas (1). Media ISP2 and R2A were the most effective for isolating Actinobacteria. One hundred and twenty-three actinobacterial strains clustered into 21 genera identified by 16S rDNA gene sequencing, most of which were from the genus Microbacterium, followed by Pseudonocardia, Streptomyces, Kocuria, Aeromicrobium, Brachybacterium and Nocardiopsis, constituted 82% of total actinobacterial isolates. By using the minimal medium, 92 actinobacterial isolates showed antimicrobial activities, and 51 strains displayed moderate to strong antimicrobial activity that inhibited the growth of more than half of the bacteria tested in this study. Functional genes related to secondary metabolites were screened, revealing that 10% (12/123) of actinobacterial isolates contained PKS-KS genes, 18% (22/123) harbored NRPS-A genes and 6% (7/123) had hybrid PKS-NRPS gene clusters. The sponges Haliclona sp., Callyspongia sp. and Desmacella sp., belonging to class Demonspongiae, and Leucaltis sp. from the class Calcarea, were dominant hosts, harboring the most diverse actinobacterial genera with stronger antimicrobial activities and more diverse PKS/NRPS genes.

Biological and Chemical Diversity of Marine Sponge-Derived Microorganisms over the Last Two Decades from 1998 to 2017

Marine sponges are well known as rich sources of biologically natural products. Growing evidence indicates that sponges harbor a wealth of microorganisms in their bodies, which are likely to be the true producers of bioactive secondary metabolites. In order to promote the study of natural product chemistry and explore the relationship between microorganisms and their sponge hosts, in this review, we give a comprehensive overview of the structures, sources, and activities of the 774 new marine natural products from sponge-derived microorganisms described over the last two decades from 1998 to 2017.

Coral and Coral-Associated Microorganisms: A Prolific Source of Potential Bioactive Natural Products

Marine invertebrates and their associated microorganisms are rich sources of bioactive compounds. Among them, coral and its associated microorganisms are promising providers of marine bioactive compounds. The present review provides an overview of bioactive compounds that are produced by corals and coral-associated microorganisms, covering the literature from 2010 to March 2019. Accordingly, 245 natural products that possess a wide range of potent bioactivities, such as anti-inflammatory, cytotoxic, antimicrobial, antivirus, and antifouling activities, among others, are described in this review.

The Biotechnological Potential of Secondary Metabolites from Marine Bacteria

Marine habitats are a rich source of molecules of biological interest. In particular, marine bacteria attract attention with their ability to synthesize structurally diverse classes of bioactive secondary metabolites with high biotechnological potential. The last decades were marked by numerous discoveries of biomolecules of bacterial symbionts, which have long been considered metabolites of marine animals. Many compounds isolated from marine bacteria are unique in their structure and biological activity. Their study has made a significant contribution to the discovery and production of new natural antimicrobial agents. Identifying the mechanisms and potential of this type of metabolite production in marine bacteria has become one of the noteworthy trends in modern biotechnology. This path has become not only one of the most promising approaches to the development of new antibiotics, but also a potential target for controlling the viability of pathogenic bacteria.

New Antibacterial Bagremycins F and G from the Marine-Derived Streptomyces sp. ZZ745

As part of our research to discover novel bioactive natural products from marine microorganisms, five bagremycin analogues, including the previously unreported bagremycins F (1) and G (2), were isolated from a marine actinomycete Streptomyces sp. ZZ745. The structures of these compounds were determined by means of NMR spectroscopic analysis, HRESIMS data, and optical rotation. Both bagremycins F (1) and G (2) showed antibacterial activity against Escherichia coli, with MIC values of 41.8 and 61.7 μM, respectively.

Antimicrobial activity of bacteria isolated from Red Sea marine invertebrates

Marine invertebrates-associated microorganisms were considered to be important sources of marine bioactive products. This study aims to isolate marine invertebrates associated bacteria with antimicrobial activity from the Red Sea and test their biosynthetic potential through the detection of PKS and NRPS gene clusters involved with the production of bioactive secondary metabolites. In this respect, fifty bacterial strains were isolated from eight different Red Sea marine invertebrates and screened for their antimicrobial activity against standard pathogenic bacteria (Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, Bacillus subtilis ATCC 6633) and yeast (Candida albicans ATCC 10231) using the standard well diffusion assay. Five isolates showed antifungal activity against Candida albicans with no activity recorded against other pathogenic bacterial strains. On the other hand when these isolates were screened for the presence of biosynthetic gene clusters (PKS and NRPS) by PCR using five sets of degenerative primers, 60% of the isolates were shown to contain at least one type of PKS and NRPS gene clusters, which indicates the biosynthetic potential of these isolates even if the isolates didn't express any biological activity in vitro. Moreover the 16S rRNA molecular identification of the isolates reveal the biodiversity of the red sea marine invertebrates associated bacteria as they were found to belong to several bacterial groups present in Alphaproteobacteria, Gammaproteobacteria, Actinobacteria and Firmicutes.

A unique indolizinium alkaloid streptopertusacin A and bioactive bafilomycins from marine-derived Streptomyces sp. HZP-2216E

Streptopertusacin A, a unique indolizinium alkaloid existing as a zwitterion, and six bafilomycins including two previously undescribed ones of 21,22-en-bafilomycin D and 21,22-en-9-hydroxybafilomycin D were isolated from a culture of the seaweed-derived Streptomyces sp. HZP-2216E. Structures of these isolated compounds were determined based on extensive NMR spectroscopic analyses, HRESIMS and MS-MS data. The stereochemical assignments were achieved by NOE information, chemical degradation, Marfey's method, and electronic circular dichroism (ECD) calculation. Streptopertusacin A is the first example of this type of indolizinium alkaloid from microorganisms and showed moderate activity against the growth of methicillin-resistant Staphylococcus aureus (MRSA). 21,22-en-bafilomycin D and 21,22-en-9-hydroxybafilomycin D had potent activities in inhibiting the proliferation of glioma cells and the growth of MRSA.